1. Field of the Invention
The invention relates to a solenoid operated valve for controlling liquid or gasiform media, comprising a solenoid and at least two media ports, which can be opened and closed by an armature.
The invention may be applied in medical technology, e.g. in dialysis machines and analyzers, and in ink jet printers. Furthermore it may be applied in a plurality of fields where aggressive or delicate media are controlled by solenoid operated valves.
2. Description of the Background Art
Conventional solenoid operated valves use magnetic systems with an armature whose movement actuates an elastomer sealing element sealing and releasing valve seats. In the power-off state the armature's position is held by a compression spring or by a tension spring. High mechanical precision of some of the valve's components is required in order to provide characteristics like positioning accuracy relative to the sealing element, stop cushioning and an accurately defined path-force characteristic. In order to achieve a satisfactory service life these systems require further measures such as an anti-corrosion coating, splash-proof water protection and anti-friction coating. All these measures cause high manufacturing costs.
A desirable feature of these solenoid operated valves is to separate the medium to be controlled from the solenoid system. Conventional approaches often eliminate the media separation feature for a simpler design or to avoid implementation difficulties when miniaturizing the valves. Drawbacks of embodiments without media separation, such as large clearance volume, poor rinsing characteristics, media warming, corrosion, and jamming of the armature, are caused by the presence of the medium itself.
In conventional approaches that avoid these drawbacks, movable separating elements for sealing the fluid to be controlled by the drive system were used. For example such separating elements may be plastic, elastomeric, or metal bellows. The actuation movement is transferred to the sealing element in the valve body by distorting the separating element. These high-value separating elements are critical components since they are distorted in every switch cycle. In case of failure the medium may leak from the valve. The repeatable function of the valve is affected by the forces required for distortion and the dependence from pressure, temperature and previous history.
Furthermore conventional arrangements require a relatively large clearance volume. Valves without media separation have a large clearance volume and poor rinsing characteristics because the complex, labyrinthine magnetic system is moistened by the fluid. Valves with media separation have unfavorable clearance volume and rinsing facilities because of the usual bellows.